Wireless communication is the transfer of information over a distance without the use of electrical conductors or “wires”. This transfer is actually the communication of electromagnetic waves between a transmitting entity and remote receiving entity. The communication distance can be anywhere from a few inches to thousands of miles.
While once relegated to large-scale applications, such as television and radio broadcasts, wireless communication is now an inescapable aspect of virtually every aspect of life. For instance, automobiles have wireless door openers, wireless alarm activators, wireless location devices, e.g. LoJack (a trademark of the LoJack Corporation of Westwood, Massachusetts), and wireless services, e.g. OnStar (a trademark of the General Motors Corporation of Detroit, Michigan). Of course cellular phones operate wirelessly, but in addition, almost all land-line telephones are now sold with wireless handsets. Wireless communication is utilized in a myriad of other applications. One example is a wireless scanning device, used for applications such as keeping tack of delivered packages or conducting inventory counts, that wirelessly communicates scanned and other information back to a main processing station.
Wireless communication is made possible by antennas that radiate and receive the electromagnetic waves to and from the air, respectively. The function of the antenna is to “match” the impedance of the propagating medium, which is usually air or free space, to the source that supplies the signals sent or interprets the signals received. Antenna designers are constantly balancing antenna size against antenna performance. These two characteristics are generally inversely proportional. To overcome the performance losses associated with fitting antennas in smaller footprints, designers have found ways to make the antennas electrically appear taller than they are physically. A few examples of these designs are inverted “F” antennas, planar inverted “F” antennas, inverted “L” antennas, “H” antennas, “J” antennas, and others. The letters used to identify these designs describe, in a general way, the actual shape of the elements used to radiate and receive the signals. These elements are often fabricated in the prior art as slot antennas, which requires a specific conductive antenna structure with gaps between the conductive areas. In applications with little space, providing these gaps is inefficient.
Often, wireless devices have a need for communication in multiple frequency bands. To maximize efficiency, a separate antenna, each tuned for its respective frequency band, is provided in a wireless device. One common issue with dual-band antennas is “isolation” between the antennas. Isolation describes the effect one antenna has on an adjacent antenna. Antennas located in close proximity often require expensive and space-consuming filters to provide adequate isolation.
Therefore, a need exists to overcome the problems with the prior art as discussed above.